Nondestructive inspection technologies for the cast stainless steel piping

Cast austenitic stainless steels (CASS) are widely used in reactor coolant piping systems in Japanese Pressurized Water Reactors (PWRs). The Japan Society of Mechanical Engineers Code requires periodic ultrasonic inspections for welds in the piping systems as in-service inspection programs. However, it is well known that coarse grained and anisotropic crystal structures in the CASS make it difficult to detect and size the flaws by ultrasonic inspection technique. Under such circumstances, Japan Nuclear Energy Safety Organization has been carrying out a five year research project entitled 'Nondestructive Inspection Technologies for the Cast Stainless Steel Piping' since 2009FY. The objectives of the project are, 1) to comprehend the unique ultrasound propagation into the CASS piping such as beam skewing and unexpected attenuation, 2) to verify the detection and sizing capabilities of flaw using ultrasonic inspection techniques and making sure the adequacy of current in-service inspection requirement from the regulatory perspective, 3) to establish the knowledge base and simulation tool to be used by inspectors and reviewers for their technical reviews. In this research project, verification of ultrasonic inspection techniques on the cast stainless steel welded joint specimens, whose material, size, dimension and welding method are identical to the actual PWR plant, is performed. Fundamental characteristics including visualizations of ultrasound propagation in the cast stainless steel are also studied to understand the unique phenomenon of the wave propagation such as beam skewing, dispersion, attenuation and so on. This report presents the preliminary results of the research project. (author)